Documents of an extremely sensitive nature and items having a high proprietary value often need to be stored within a safe or other structure. The structure typically includes a lock mechanism, and the structure is generally designed to be accessible only by a select few individuals who are entrusted with a predetermined combination code that facilitates the unlocking of the mechanism. Unauthorized persons will use simple lock picking tools as well as sophisticated equipment that can apply high mechanical forces or an electric or magnetic field to the lock mechanism in order to manipulate the components within the lock mechanism.
As the tools utilized in lock picking have become more sophisticated, lock mechanisms have been improved to resist these sophisticated lock picking methods. Mechanical and/or electrical elements have been used in locks to provide complicated barriers to a potential unauthorized person attempting to break into the structure. However, unauthorized persons continue to attack even these improved lock mechanisms, including drilling into the interior of the lock mechanism through lock casing openings. Locations on the lock casing that are subject to frequent attack include the mounting bolts and the spindle mount where a spindle shaft from the combination dial enters the lock casing.
Additionally, unauthorized persons attempting to break into the structure have been known to use devices that apply high acceleration to the combination dial in order to overcome security elements of the lock mechanism. The high accelerations of the gear train can sometimes force the gears controlling a lock bolt to rotate and unlock the lock mechanism without a proper combination entry. These high acceleration devices can include so-called auto-dialers, which rapidly attempt every possible combination until the proper combination has been detected. Even if the unauthorized person is unsuccessful at opening the lock mechanism in this manner, the rapid collisions of gear teeth in a gear train caused by high acceleration can frequently damage the gear train and lead to improper operations of the lock mechanism. The collisions of the gear teeth may also provide audible information that an unauthorized person can detect and use to determine the programmed combination that actuates the unlocking of the mechanism.
Furthermore, improved lock mechanisms must comply with highly stringent government specifications in order to be used on government-controlled structures and containment devices. For example, the stringency of relevant U.S. government specifications is readily appreciated from Federal Specification FF-L-2740, dated Oct. 12, 1989, titled “FEDERAL SPECIFICATION: LOCKS, COMBINATION” for the use of all federal agencies. Section 3.4.7, “Combination Redial,” requires that once the lock bolt has been extended to its locked position “it shall not be possible to reopen the lock without completely redialing the locked combination.” Section 3.6.1.3, “Emanation Analysis,” requires that the lock shall not emit any sounds or other signals which may be used to surreptitiously open the lock within a specified period. Further U.S. government requirements are included in Federal Specification FF-L-2937, dated Jan. 31, 2005, titled “FEDERAL SPECIFICATION: COMBINATION LOCK, MECHANICAL.” In that document, Section 4.7.4, “Endurance Test,” requires that a sample lock be “cycled through fifty combination changes including three open and close verifications after each change” to ensure proper combination setting functionality. Section 4.7.7, “Resistance to Unauthorized Opening Test,” requires that the lock cannot be opened by mechanical manipulation or autodialing of a computer-assisted device for at least a period of 20 hours.
Consequently, it would be desirable to improve on a high security lock to address the frequently-attacked areas of the lock mechanism while remaining in full compliance with typical government specifications.